Limitation of Noise on Light Detectors using an Aperture

ABSTRACT

The present disclosure relates to limitation of noise on light detectors using an aperture. One example embodiment includes a system. The system includes a lens disposed relative to a scene and configured to focus light from the scene onto a focal plane. The system also includes an aperture defined within an opaque material disposed at the focal plane of the lens. The aperture has a cross-sectional area. In addition, the system includes an array of light detectors disposed on a side of the focal plane opposite the lens and configured to intercept and detect diverging light focused by the lens and transmitted through the aperture. A cross-sectional area of the array of light detectors that intercepts the diverging light is greater than the cross-sectional area of the aperture.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Light detectors, such as photodiodes, single photon avalanche diodes(SPADs), or other types of avalanche photodiodes (APDs), can be used todetect light that is imparted on their surfaces (e.g., by outputting anelectrical signal, such as a voltage or a current, corresponding to anintensity of the light). Many types of such devices are fabricated outof semiconducting materials, such as silicon. In order to detect lightover a substantial geometric area, multiple light detectors can bearranged into arrays connected in parallel. These arrays are sometimesreferred to as silicon photomultipliers (SiPMs) or multi-pixel photoncounters (MPPCs).

Some of the above arrangements are sensitive to relatively lowintensities of light, thereby enhancing their detection qualities.However, this can lead to the above arrangements also beingdisproportionately susceptible to adverse background effects (e.g.,extraneous light from outside sources could affect a measurement by thelight detectors). As such, a method or device for reducing thebackground effects affecting the light detection could increase theaccuracy of measurements made by such light detectors.

SUMMARY

The specification and drawings disclose embodiments that relate to alimitation of noise on light detectors using an aperture.

An example light detection system may include a lens, an aperture, andan array of light detectors. The aperture may be placed at the focalplane of the lens, and the lens may focus light scattered by an objectwithin a scene. The aperture may limit the amount of light transmittedto the array of light detectors by limiting the amount of lighttransmitted at the focal plane of the lens. By limiting the amount oflight transmitted through the aperture, the aperture may reduce thebackground light transmitted to the array. After passing through theaperture, the light may diverge as the light approaches the array. Thelight may then be intercepted and detected by a portion of the lightdetectors within the array. By allowing the light to diverge afterpassing through the aperture, the detection area of the array isincreased when compared to the same cross-section of the light at thefocal plane (i.e., the cross-section of the detection area of the arrayis larger than the cross-section of the aperture). Thus, more lightdetectors can be spread across the detection area, thereby increasingthe dynamic range, sensitivity, or imaging resolution of the array oflight detectors.

In a first aspect, the disclosure describes a system. The systemincludes a lens disposed relative to a scene and configured to focuslight from the scene onto a focal plane. The system also includes anaperture defined within an opaque material disposed at the focal planeof the lens. The aperture has a cross-sectional area. The system furtherincludes an array of light detectors disposed on a side of the focalplane opposite the lens and configured to intercept and detect diverginglight focused by the lens and transmitted through the aperture. Across-sectional area of the array of light detectors that intercepts thediverging light is greater than the cross-sectional area of theaperture.

In a second aspect, the disclosure describes a method. The methodincludes focusing, by a lens disposed relative to a scene, light fromthe scene onto a focal plane. The method also includes transmitting,through an aperture defined within an opaque material disposed at thefocal plane of the lens, the light from the scene. The aperture has across-sectional area. The method further includes diverging, by thelight from the scene transmitted through the aperture. In addition, themethod includes intercepting, by an array of light detectors disposed ona side of the focal plane opposite the lens, the diverged light from thescene. A cross-sectional area of the array of light detectors thatintercept the diverged light from the scene is greater than thecross-sectional area of the aperture. The method additionally includesdetecting, by the array of light detectors, the intercepted light.

In a third aspect, the disclosure describes a light detection andranging (LIDAR) device. The LIDAR device includes a LIDAR transmitterconfigured to illuminate a scene with light. The LIDAR device alsoincludes a LIDAR receiver configured to receive light scattered by oneor more objects within the scene to map the scene. The LIDAR receiverincludes a lens configured to focus the light scattered by the one ormore objects within the scene onto a focal plane. The LIDAR receiveralso includes an aperture defined within an opaque material disposed atthe focal plane. The aperture has a cross-sectional area. The LIDARreceiver further includes an array of light detectors disposed on a sideof the focal plane opposite the lens and configured to intercept anddetect diverging light focused by the lens and transmitted through theaperture. A cross-sectional area of the array of light detectors thatintercepts the diverging light is greater than the cross-sectional areaof the aperture.

In an additional aspect, the disclosure describes a system. The systemincludes a means for focusing light from a scene onto a focal plane. Themeans for focusing is disposed relative to the scene. The system alsoincludes a means for transmitting, through an aperture defined within anopaque material disposed at the focal plane of the lens, the light fromthe scene. The aperture has a cross-sectional area. The system furtherincludes a means for diverging the light from the scene transmittedthrough the aperture. In addition, the system includes a means forintercepting the diverged light from the scene. The means forintercepting is disposed on a side of the focal plane opposite the meansfor focusing. A cross-sectional area of the means for intercepting thatintercept the diverged light from the scene is greater than thecross-sectional area of the aperture. The system additionally includes ameans for detecting the intercepted light.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the figures and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is an illustration of a noise limiting system that includes anaperture, according to example embodiments.

FIG. 1B is an illustration of a noise limiting system that includes anaperture, according to example embodiments.

FIG. 2 is an illustration of a noise limiting LIDAR device that includesan aperture, according to example embodiments.

FIG. 3 is an illustration of a noise limiting system that includes anaperture, according to example embodiments.

FIG. 4 is an illustration of a noise limiting system that includes anaperture, according to example embodiments.

FIG. 5 is an illustration of a noise limiting system that includes anaperture, according to example embodiments.

FIG. 6A is an illustration of an opaque material with various aperturesdefined therein, according to example embodiments.

FIG. 6B is an illustration of a portion of a noise limiting system thatincludes apertures, according to example embodiments.

FIG. 7A is an illustration of an opaque material with a resizableaperture, according to example embodiments.

FIG. 7B is an illustration of an opaque material with a resizableaperture, according to example embodiments.

FIG. 8 is an illustration of an opaque material with an aperture havingan adjustable location, according to example embodiments.

FIG. 9 is a flow diagram of a method, according to example embodiments.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodimentor feature described herein is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the figures should notbe viewed as limiting. It should be understood that other embodimentsmight include more or less of each element shown in a given figure. Inaddition, some of the illustrated elements may be combined or omitted.Similarly, an example embodiment may include elements that are notillustrated in the figures.

I. Overview

Example embodiments may relate to devices, systems, and methods forreducing background light imparted onto an array of light detectors. Thelight detectors in the array may be sensing light from a scene (e.g.,the light detectors may be a sensing component of a LIDAR system).

One example system can include a lens. The lens may be used to focuslight from a scene onto a focal plane. However, the lens may also focusbackground light not intended to be observed onto the focal plane (e.g.,sunlight within the scene). In order to selectively filter the light(i.e., separate background light from light corresponding to informationwithin the scene), an opaque material (e.g., selectively etched metal ora glass substrate with a mask placed over it) may be placed at the focalplane of the lens. The opaque material could be a slab, a sheet, orvarious other shapes in a variety of embodiments. Within the opaquematerial, an aperture may be defined. The aperture may select a regionof, or the entirety of, the light of the scene focused by the lens ontothe focal plane.

On a backside of the opaque material (i.e., a side of the opaquematerial opposite the lens), the light selected by the aperture maydiverge from the aperture. In the direction of divergence of the light,the system may include an array of light detectors (e.g., SPADs)disposed some distance from the aperture. This array of light detectorsmay detect the diverging light (e.g., an intensity of the diverginglight). Because the light is diverging, the number of light detectorsable to fit into a detection area can be larger than could fit in adetection area corresponding to the same cone of light at the focalplane of the lens. This is due to the fact that the detection area wouldbe more tightly focused, and thus smaller, at the focal plane of thelens than at a distance displaced from the aperture. As an example, anaperture having a cross-sectional area of 200 μm by 200 μm may occupy anequivalent area to hundreds of SPADs (e.g., each SPAD having across-sectional area between 200 μm² and 600 μm²). By comparison, if thelight diverges away from the aperture to a distance corresponding to acircular cross-sectional area having a diameter of 1.33 mm, thedetection area, at that plane, may occupy an equivalent area tothousands or tens of thousands of SPADs.

Further, the distance by which the light detector array is displacedfrom the aperture (i.e., the distance the light detector array isdisplaced from the focal plane of the lens) can vary in variousembodiments. The number of light detectors positioned to detect thelight diverging from the aperture may be increased by increasing thedistance between the light detector array and the aperture. For example,for scenes that have an increased amount of background light, the lightdetector array could be displaced an increased distance from theaperture.

Additionally, in some embodiments, the aperture may be adjustable. Forexample, the cross-sectional area of the aperture could be varied. Insome embodiments, the cross-sectional area may be defined by an iristhat can open or close to increase or decrease the opening within theopaque material that defines the aperture. Alternatively, the aperturemay be a slit within the opaque material that is partially covered by aretractable shade. The retractable shade could be retracted or extendedto alter the amount of light transmitted through the aperture, and thus,change the effective cross-sectional area of the aperture. Even further,the opaque material may have multiple apertures defined therein. Themultiple apertures may have different shapes and/or sizes. Further, thesystem could include one or more mirrors (e.g., microelectromechanicalsystems, MEMs, mirrors) that reflect light from the lens toward theopaque material. The one or more mirrors could change angle with respectto the lens or could change orientation such that a different one of themirrors was in the path of the light focused by the lens. This couldallow a different one of the apertures defined within the opaquematerial to be selected, thereby changing the effective aperture area.

II. Example Systems

FIG. 1A is an illustration of a noise limiting system 100 that includesan aperture, according to example embodiments. The system 100 mayinclude an array 110 of light detectors 112, an aperture 122 definedwithin an opaque material 120, and a lens 130. The system 100 maymeasure light 102 scattered by an object 140 within a scene. The light102 may also come, at least partially, from background sources. Thenoise limiting system 100 may be a part of a LIDAR device (e.g., a LIDARreceiver), in various embodiments. For example, the LIDAR device may beused for navigation of an autonomous vehicle. Further, in someembodiments, the noise limiting system 100, or portions thereof, may becontained within an area that is unexposed to exterior light other thanat the lens 130 or aperture 122. This may prevent ambient light fromtriggering the light detectors 112 and adversely affecting anymeasurements.

The array 110 is an arrangement of the light detectors 112. In variousembodiments, the array 110 may have different shapes. As illustrated inFIG. 1A, the array 110 may have a rectangular or a square shape. Inalternate embodiments, the array 110 may be circular. The size of thearray 110 may correspond to a cross-sectional area of the light 110diverging from the aperture 122, based on the distance the array 110 ispositioned from the aperture 122. In some embodiments, the array 110 maybe movable. The array 110 may be moveable closer to, or further from,the aperture 122. For example, the array may be on an electrical stagecapable of translating in one, two, or three dimensions.

Further, the array 110 may have one or more outputs to a computingdevice. The computing device (e.g., a microprocessor) may receiveelectrical signals from the array 110 which indicate an intensity of thelight 102 incident on the light detectors 112. The computing device mayuse the electrical signals to determine information about the object 140(e.g., distance of the object 140 from the aperture 122). In embodimentswhere there is a single connection between the array 110 and thecomputing device, the light detectors 112 within the array 110 may beinterconnected with one another in parallel. As such, the array 110 maybe an SiPM or an MPPC, depending on the particular arrangement and typeof the light detectors 112 within the array 110.

The light detectors 112 may be one of a variety of types. For example,the light detectors 112 may be SPADs. SPADs may make use of avalanchebreakdown within a reverse biased p-n junction (i.e., diode) to increaseoutput current for a given incident illumination on the photodetector.Further, SPADs may be able to generate multiple electron-hole pairs fora single incident photon. In alternate embodiments, the light detectors112 may be APDs. Both APDs and SPADs may be biased above the avalanchebreakdown voltage. Such a biasing condition may create a positivefeedback loop having a loop gain that is greater than one. Thus, APDsand SPADs biased above the threshold avalanche breakdown voltage may besingle photon sensitive. In still other embodiments, the light detectors112 may be photoresistors, charge-coupled devices (CCDs), orphotovoltaic cells.

In various embodiments, the array 110 may include more than one type oflight detector across the array. For example, if multiple wavelengthsare being detected by the array 110, the array 110 may comprise someSPADs that are sensitive to one range of wavelengths and some SPADs thatare sensitive to a different range of wavelengths. In some embodiments,the light detectors 110 may be sensitive to wavelengths between 400 nmand 1.6 μm (visible and infrared wavelengths). Further the lightdetectors 110 may have various sizes and shapes within a givenembodiment or across various embodiments. In example embodiments, thelight detectors 112 may be SPADs that have package sizes that are 1%,0.1%, or 0.01% of the area of the array 110.

The opaque material 120 may block the light 102 from the scene (e.g.,background light) that is focused by the lens 130 from being transmittedto the array 110. As such, the opaque material 120 may be configured toblock certain background light that could adversely affect the accuracyof a measurement performed by the array 110 of light detectors 112. Theopaque material 120, and therefore the aperture 122, may be positionedat or near a focal plane of the lens 130. The opaque material 120 mayblock transmission by absorbing the light 102. Additionally oralternatively, the opaque material 120 may block transmission byreflecting the light 102. In some embodiments, the opaque material 120may be etched metal. In alternate embodiments, the opaque material 120may be a polymer substrate, a biaxially-oriented polyethyleneterephthalate (BoPET) sheet (also referred to as a Mylar® sheet), or aglass overlaid with an opaque mask. Other opaque materials are alsopossible in various alternate embodiments.

The aperture 122 provides a port within the opaque material 120 throughwhich the light 102 may be transmitted. The aperture 122 may be definedwithin the opaque material 120 in a variety of ways. For example, if theopaque material 120 is a metal, the metal may be etched to define theaperture 122. Alternatively, if the opaque material 120 is a glasssubstrate overlaid with a mask, the mask may include an aperture 122defined using photolithography. In various embodiments, the aperture 122may be partially or wholly transparent. For example, if the opaquematerial 120 is a glass substrate overlaid with a mask, the aperture 122may be defined by the portion of the glass substrate not covered by themask, meaning the aperture 122 is not completely hollow, but rather ismade of glass. Therefore, the aperture 122 may be nearly, but notentirely, transparent to the wavelengths of the light 102 scattered bythe object 140 (because most glasses are not 100% transparent).

The aperture 122 (in conjunction with the opaque material 120) mayperform to spatially filter the light 102 from the scene at the focalplane. For example, the light 102 may be focused onto the focal plane ata surface the opaque material 120, and the aperture 122 may allow only aportion of the focused light to be transmitted to the array 110. As suchthe aperture 122 may behave as an optical pinhole. In exampleembodiments, the aperture may have a cross-sectional area of between0.02 mm² and 0.06 mm² (e.g., 0.04 mm²).

Although the term “aperture” as used above with respect to the aperture122 describes a recess or hole in an opaque material through which lightmay be transmitted, it is understood that the term “aperture” mayinclude a broad array of optical features. For example, as usedthroughout the description and claims, the term “aperture” mayadditionally encompass transparent or translucent structures definedwithin an opaque material through which light can be partiallytransmitted. Further, the term “aperture” may describe a structure thatotherwise selectively limits the passage of light (e.g., throughreflection or refraction), such as a mirror surrounded by an opaquematerial. In one example embodiment, mirrored arrays surrounded by anopaque material may be arranged to reflect light in a certain direction,thereby defining a reflective portion. This reflective portion may bereferred to as an “aperture”.

The lens 130 may focus the light 102 from the scene onto the focal plane(e.g., where the aperture 122 is positioned). In this way, the lightintensity collected from the scene, at the lens 130, may be maintainedwhile reducing the cross-sectional area over which the light 102 isbeing projected (i.e., increasing the spatial power density of the light102). As such, the lens 130 may be a converging lens. As illustrated inFIG. 1A, the lens 130 may be a biconvex lens. For example, the lens maybe a spherical lens. In alternate embodiments, the lens may be aconsecutive set of lens positioned one after another (e.g., a biconvexlens that focuses light in a first direction and an additional biconvexlens that focuses light in a second plane that is orthogonal to thefirst direction). Other types of lenses are also possible. In addition,there may be other free space optics (e.g., mirrors) positioned near thelens 130 to aid in focusing the light 102 incident on the lens 130 ontothe opaque material 120.

The object 140 may be any object positioned within a scene surroundingthe noise limiting system 100. If the noise limiting system 100 is acomponent of a receiver of a LIDAR system, the object 140 may beilluminated by a transmitter of the same LIDAR system using the light102. In example embodiments where the LIDAR system is used fornavigation on an autonomous vehicle, the object 140 may be pedestrians,other vehicles, obstacles (e.g., trees), or road signs.

The light 102, as described above, may be produced by a transmitterwithin a LIDAR device. As illustrated, the light 102 may be scattered bythe object 140, focused by the lens 130, transmitted through theaperture 122 in the opaque material 120, and measured by the array 110of light detectors 112. This sequence may occur (e.g., within a LIDARdevice) to determine something about the object 140. In someembodiments, the light measured by the array may instead be light thatscattered from multiple objects or from no objects (e.g., lighttransmitted by a transmitter of a LIDAR device is not reflected backtoward the LIDAR device, so the lens only focuses ambient light, such assunlight).

In addition, the wavelength of the light 102 used to analyze the object140 may be tailored based on the types of objects expected to be withina scene and their expected distance from the lens 130. For example, ifthe objects expected to be within the scene absorb all incoming light of500 nm wavelength, a wavelength other than 500 nm may be selected toilluminate the object 140 and to be analyzed by the noise limitingsystem 100. The wavelength of the light 102 (e.g., if transmitted by atransmitter of a LIDAR device) may correspond to a source that generatesthe light 102. For example, if the light is generated by a diode laser,the light 102 may be of a wavelength range centered on 900 nm. Amultitude of different sources may be capable of generating the light102 (e.g., an optical fiber amplifier, various types of lasers, abroadband source with a filter, etc.).

FIG. 1B is an illustration of the noise limiting system 100 illustratedin FIG. 1A. As indicated, the distance between the object 140 and thelens 130 is ‘d’, the distance between the lens 130 and the opaquematerial 120 (with a rectangular aperture 126 defined therein, asopposed to the round aperture 122 illustrated in FIG. 1A) is ‘f’, andthe distance between the opaque material 120 and the array 110 is ‘x’.In the embodiment illustrated, the opaque material 120 and aperture 126may be positioned at the focal plane of the lens (i.e., ‘f’ may beequivalent to the focal length of the lens). Further, there may be afilter 160 placed between the lens 130 and the opaque material 120. Alsolocated at a distance ‘d’ from the object 140 is an emitter 150 (e.g., alaser with a LIDAR transmitter) that emits a signal to be measured bythe array 110.

The following is a mathematical illustration comparing the amount ofbackground light that is detected by the array 110 to the amount ofsignal light that is detected by the array 110. For the sake ofillustration, it is assumed that the object 140 is fully illuminated bysunlight at normal incidence, where the sunlight represents a backgroundlight source. Further, it is assumed that all the light that illuminatesthe object 140 is scattered according to Lambert's cosine law. Inaddition, it is assumed that all of the light (both background andsignal) that reaches the plane of the array 110 is fully detected by thearray 110.

The power of the signal, emitted by the emitter 150, that reaches theaperture 124, and thus the array 110, can be calculated using thefollowing:

$P_{signal} = {P_{tx} \times \Gamma \times \frac{A_{lens}}{\pi \; d^{2}}}$

where P_(signal) represents the radiant flux (e.g., in W) of the opticalsignal emitted by the emitter 150 that reaches the array 110, P_(tx)represents the power (e.g., in W) transmitted by the emitter 150, Frepresents the reflectivity of the object 140 (e.g., taking into accountLambert's Cosine Law), and A_(lens) represents the cross-sectional areaof the lens 130.

In addition, the background light that reaches the lens 130 can becalculated as follows:

${\overset{\_}{P}}_{background} = \frac{{\overset{\_}{P}}_{sun} \times T_{filter}}{\pi}$

where P _(background) represents the radiance

$\left( {{e.g.},{{in}\mspace{14mu} \frac{W}{m^{2} \cdot {sr}}}} \right)$

of background signal caused by sunlight scattering off the object 140arriving on the lens 130 that is within a wavelength band that will beselectively passed by the filter 160, P _(sun) represents the irradiance

$\left( {{e.g.},{{in}\mspace{14mu} \frac{W}{m^{2}}}} \right)$

density due to the sun (i.e., the background source), and T_(filter)represents the transmission coefficient of the filter 160 (e.g., abandpass optical filter). The factor of

$\frac{1}{\pi}$

comes in due to the assumption of Lambertian scattering off of theobject 140 from normal incidence.

The aperture 124 reduces the amount of background light permitted to betransmitted to the array 110. To calculate the power of the backgroundlight that reaches the array 110, after being transmitted through theaperture 124, the area of the aperture 124 is taken into account. Thecross-sectional area of the aperture can be calculated using thefollowing:

A _(aperture) =w×h

where A_(aperture) represents the surface area of the aperture 126relative to the object 140, and w and h represent the width and heightof the aperture 124, respectively. In addition, if the lens 130 is acircular lens, the cross-sectional area of the lens is:

$A_{lens} = {\pi \left( \frac{d_{lens}}{2} \right)}^{2}$

where d_(lens) represents the diameter of the lens.

To calculate the background power transmitted to the array 110 throughthe aperture 124, the following can be used:

$P_{background} = {{\overset{\_}{P}}_{background} \times \frac{A_{aperture}}{f^{2}} \times A_{lens}}$

where P_(background) represents background power incident on the array110, and

$\frac{A_{aperture}}{f^{2}}$

represents the acceptance solid angle in steradians. The above formulashows that P_(background) is the amount of radiance in the backgroundsignal after being reduced by the lens 130 and then the aperture 124.

Substituting the above determined values in for P _(background),A_(aperture), and A_(lens) the following can be derived:

$P_{background} = {{\left( \frac{{\overset{\_}{P}}_{sun}T_{filter}}{\pi} \right) \times \left( \frac{wh}{f^{2}} \right) \times \left( {\pi \left( \frac{d_{lens}}{2} \right)}^{2} \right)} = {{\overset{\_}{P}}_{sun}T_{filter}{wh}\frac{d_{lens}^{2}}{4\; f^{2}}}}$

Further, the quantity

$\frac{f}{d_{lens}}$

may be referred to as the “F number” of the lens 130. Thus, with onemore substitution, the following can be deduced for background power:

$P_{background} = \frac{{\overset{\_}{P}}_{sun}T_{filter}{wh}}{4\; F^{2}}$

Making similar substitutions, the following can be deduced for signalpower transmitted from the emitter 150 that arrives at the array 110:

$P_{signal} = {{P_{tx} \times \Gamma \times \frac{{\pi \left( \frac{d_{lens}}{2} \right)}^{2}}{\pi \; d^{2}}} = \frac{P_{tx}\Gamma \; d_{lens}^{2}}{4\; d^{2}}}$

By comparing P_(signal) with P_(background), a signal to noise ratio(SNR) may be determined. As demonstrated, an inclusion of the aperture124, particularly for apertures having small w and/or small h, thebackground power can be significantly reduced with respect to the signalpower. Besides reducing aperture area, increasing the transmitted powerby the emitter 150, decreasing the transmission coefficient (i.e.,reducing an amount of background light that gets transmitted through thefilter), and increasing the reflectivity of the object 140 may be waysof increasing the SNR. In the case of a pulsed signal, the shot noise ofthe background, as opposed to the power of the background, may beprimarily relevant when computing the SNR.

As described above, the light transmitted through the aperture 124 maydiverge as it approaches the array 110. Due to the divergence, thedetection area at the array 110 of light detectors may be larger thanthe cross-sectional area of the aperture 124 at the focal plane. Anincreased detection area (e.g., measured in m²) for a given light power(e.g., measured in W) leads to a reduced light intensity (e.g., measuredin

$\left. \frac{W}{m^{2}} \right)$

incident upon the array 110.

The reduction in light intensity may be particularly beneficial inembodiments where the array 110 includes SPADs or other light detectorshaving high sensitivities. For example, SPADs derive their sensitivityfrom a large reverse-bias voltage that produces avalanche breakdownwithin a semiconductor. This avalanche breakdown can be triggered by theabsorption of a single photon. Once a SPAD absorbs a single photon andthe avalanche breakdown begins, the SPAD cannot detect additionalphotons until the SPAD is quenched (e.g., by restoring the reverse-biasvoltage). The time until the SPAD is quenched may be referred to as therecovery time. If additional photons are arriving at time intervalsapproaching the recovery time (e.g., within a factor of ten of therecovery time), the SPAD begins to saturate, and the measurements by theSPAD may no longer directly correlate to the power of the light incidenton the SPAD. Thus, by reducing the light power incident on anyindividual light detector (e.g., SPAD) within the array 110, the lightdetectors within the array 110 (e.g., SPADs) may remain unsaturated. Assuch, the light measurements by each individual SPAD may have anincreased accuracy.

FIG. 2 is an illustration of a noise limiting LIDAR device 210 thatincludes an aperture, according to example embodiments. The LIDAR device210 may include a laser emitter 212, a computing device 214, an array110 of light detectors, an opaque material 120 with the aperture definedtherein, and a lens 130. The LIDAR device 210 may use light 102 to mapan object 140 within a scene. The LIDAR device 210 may be used within anautonomous vehicle for navigation, in example embodiments.

The laser emitter 212 may emit the light 102 which is scattered by theobject 140 in the scene and ultimately measured by the array 110 oflight detectors (e.g., the light detectors 102 illustrated in FIG. 1A).In some embodiments, the laser emitter 212 may include an optical fiberamplifier or other amplifying system to increase to power output of thelaser emitter 212. Further, the laser emitter 212 may be a pulsed laser(as opposed to a continuous wave, CW, laser), allowing for increasedpeak power while maintaining an equivalent continuous power output.

The computing device 214 may be configured to control components of theLIDAR device 210 and to analyze signals received from components of theLIDAR device 210 (e.g., the array 110 of light detectors 112). Thecomputing device 214 may include a processor (e.g., a microprocessor ofa microcontroller) that executes instructions stored within a memory toperform various actions. The computing device 214 may use timingassociated with a signal measured by the array 110 to determine alocation (e.g., the distance from the LIDAR device 210) of the object140. For example, in embodiments where the laser emitter 212 is a pulsedlaser, the computing device 214 can monitor timings of the output lightpulses and compare those timings with timings of the signal pulsesmeasured by the array 110. This comparison may allow the computingdevice 214 to compute the distance of the object 140 based on the speedof light and the time of travel of the light pulse. In order to make anaccurate comparison between the timing of the output light pulses andthe timing of the signal pulses measured by the array 110, the computingdevice 214 may be configured to account for parallax (e.g., because thelaser emitter 212 and the lens 130 are not located at the same locationin space).

In some embodiments, the computing device 214 may be configured tomodulate the laser emitter 212 of the LIDAR device 210. For example, thecomputing device 214 may be configured to change the direction ofprojection of the laser emitter 212 (e.g., if the laser emitter 212 ismounted to or includes a mechanical stage). The computing device 214 mayalso be configured to modulate the timing, the power, or the wavelengthof the light 102 emitted by the laser emitter 212. Such modulations mayinclude the addition or removal of filters from the path of the light102, in various embodiments.

Additionally, the computing device 214 may be configured to adjust thelocation of the lens 130, the opaque material 120, and the array 110relative to one another. For example, the lens 130 may be on a movablestage that is controlled by the computing device 214 to adjust tolocation of the lens 130, and thus the location of the focal plane ofthe lens 130. Further, the array 110 may be on a separate stage thatallows the array 110 to be moved relative to the opaque material 120 andthe aperture 122. The array 110 may be moved by the computing device 214to alter the detection area on the array 110. As the array 110 is movedfarther from the opaque material 120, the cross-sectional detection areaon the array 110 may increase because the light 102 diverges as thedistance from the aperture 122 is increased. Therefore, the computingdevice 214 may move the array 110 to alter the number of light detectors112 illuminated by the diverging light 102.

In some embodiments, the computing device may also be configured tocontrol the aperture. For example, the aperture may, in someembodiments, be selectable from a number of apertures defined within theopaque material. In such embodiments, a MEMS mirror located between thelens and the opaque material may be adjustable by the computing deviceto determine to which of the multiple apertures the light is directed.In some embodiments, the various apertures may have different shapes andsizes. In still other embodiments, the aperture may be defined by aniris (or other type of diaphragm). The iris may be expanded orcontracted by the computing device, for example, to control the size ofthe aperture.

FIG. 3 is an illustration of a noise limiting system 300 that includesan aperture, according to example embodiments. Similar to the system 100illustrated in FIG. 1A, the system 300 may include an array 110 of lightdetectors 112, an aperture 122 defined within an opaque material 120,and a lens 130. In addition, the system 300 may include an opticalfilter 302. The system 300 may measure light 102 scattered by an object140 within a scene. The lens 130, the opaque material 120 defined withthe aperture 122, and the array 110 of light detectors 112 may behaveanalogously as described with respect to FIG. 1A.

The optical filter 302 may be configured to divert light of particularwavelengths away from the array 110. For example, if the noise limitingsystem 300 is a component of a LIDAR device (e.g., a detector of a LIDARdevice), the optical filter 302 may divert any light away from the array110 that is not of the wavelength range emitted by a laser emitter ofthe LIDAR device. Therefore, the optical filter 302 may, at leastpartially, prevent ambient light or background light from adverselyaffecting the measurement by the array 110.

In various embodiments, the optical filter 302 may be located in variouspositions relative to the array 110. As illustrated in FIG. 3, theoptical filter 302 may be located in between the lens 130 and the opaquematerial 120. The optical filter may alternatively be located betweenthe lens and the object, between the opaque material and the array, oron the array itself (e.g., the array may have a screen covering thesurface of the array that includes the optical filter or each of thelight detectors may individually be covered by a separate opticalfilter).

The optical filter 302 may be an absorptive filter. Additionally oralternatively, the optical filter 302 may be a reflective filter. Theoptical filter 302 may selectively transmit wavelengths within a definedwavelength range (i.e., act as a bandpass optical filter, such as amonochromatic optical filter), wavelengths outside a defined wavelengthrange (i.e., act as a band-rejection optical filter), wavelengths belowa defined threshold (i.e., act as a lowpass optical filter), orwavelengths above a defined threshold (i.e., a highpass optical filter).Further, in some embodiments, multiple optical filters may be cascadedto achieve optimized filtering characteristics (e.g., a lowpass filtercascaded with a highpass filter to achieve a bandpass filtercharacteristic). The optical filter 302 may be a dichroic filter orcascaded dichroic filters, in some embodiments. In alternateembodiments, the optical filter 302 may be a diffractive filter. Adiffractive filter may split the optical path of background light andsignal light. This may allow separate background tracking, in someembodiments.

Further, the optical filter 302 may selectively transmit based onqualities of light other than wavelength. For example, the opticalfilter 302 may selectively transmit light based on polarization (e.g.,horizontally polarized or vertically polarized). Alternate types ofoptical filters are also possible.

FIG. 4 is an illustration of a noise limiting system 400 that includesan aperture, according to example embodiments. Similar to the system 100illustrated in FIG. 1A, the system 400 may include an array 110 of lightdetectors 112, an aperture 122 defined within an opaque material 120,and a lens 130. The system 400 may also include an optical diffuser 402.The system 400 may measure light 102 scattered by an object 140 within ascene. The lens 130, the opaque material 120 defined with the aperture122, and the array 110 of light detectors 112 may behave analogously asdescribed with respect to FIG. 1A.

The optical diffuser 402 may evenly distribute the power density of thelight 102 transmitted through the aperture 122 among the light detectors112 by diffusing the light 102. The optical diffuser 402 may include asandblasted glass diffuser, a ground glass diffuser, or a holographicdiffuser, in various embodiments. Other types of optical diffusers arealso possible. The optical diffuser 402 is one of a group of possiblecomponents that enhance an aspect of the divergence of the light 102once the light 102 is transmitted through the aperture 122. Otherdivergence enhancing components could include optical waveguides orfluids with non-unity indices of refraction, for example.

In various embodiments, the optical diffuser 402 may be located invarious positions relative to the array 110. As illustrated in FIG. 4,the optical diffuser 402 may be located in between the opaque material120 and the array 110. Alternatively, the optical diffuser may belocated on the array itself (e.g., the array may have a screen coveringthe surface of the array that includes the optical diffuser or each ofthe light detectors may individually be covered by a separate opticaldiffuser).

FIG. 5 is an illustration of a noise limiting system 500 that includesan aperture, according to example embodiments. Similar to the system 100illustrated in FIG. 1A, the system 500 may include an array 110 of lightdetectors 112, an aperture 122 defined within an opaque material 120,and a lens 130. The system 500 may further include mirrors 502. The lens130, the opaque material 120 defined with the aperture 122, and thearray 110 of light detectors 112 may behave analogously as describedwith respect to FIG. 1A.

The mirrors 502 may reflect any of the light 102 that is transmittedthrough the aperture 122 that is diverted away from the array 110(illustrated in FIG. 5 by the finely dashed lines). This process may bereferred to as “photon recycling.” The diversion of the light may occurdue to a reflection of the light from a face of the array 110 (e.g., dueto a partially reflective quality of faces of the light detectors 112 orfrom interstitial regions in between faces of the light detectors 112).In such a case, the mirrors 502 may redirect light reflected from theface of the array 110 back toward the array 110. Other inadvertentcauses of light diversion are also possible.

As illustrated in FIG. 5, the mirrors 502 may be curved mirrors. Inalternate embodiments there may be more or fewer mirrors. For example,in some embodiments, there may be a series of planar mirrors directingthe light toward the array. In another alternate embodiment, there mayinstead by a single hollow cylinder or hollow cone, which encapsulatesthe light path between the aperture and the array, that has a reflectiveinner surface to redirect the light toward the array. Alternatively,there could be four mirrors, as opposed to two, having the shape of themirrors 502 illustrated in FIG. 5 and positioned around the light pathbetween the aperture and the array. Further, rather than mirrors, someembodiments may include a structure in between the aperture and thearray that totally internally reflects the light traveling from theaperture to the array (e.g., the structure has an index of refractionthat is large enough compared to an index of refraction of thesurrounding material to induce total internal reflection). Such astructure may be referred to as a light-pipe. Various otherarrangements, shapes, and sizes of mirrors are also possible.

Some embodiments may include multiple features described with respect toFIGS. 3-5. For example, an example embodiment may include an opticalfilter between the lens and the opaque material, an optical diffuserbetween the opaque material and the array, and mirrors between theoptical diffuser and the array. Further, similar to the componentswithin the noise limiting LIDAR device 210 illustrated in FIG. 2, theadditional components illustrated in FIGS. 3-5 (e.g., the optical filter302, the optical diffuser 402, and the mirrors 502) may also be onmovable stages that are connectable to and controllable by a computingdevice. Other characteristics of these components (e.g., diffusivity ofthe optical diffuser 402 or angle of the mirrors 502) could also becontrolled by a computing device, in various embodiments.

FIG. 6A is an illustration of an opaque material 610 with variousapertures defined therein, according to example embodiments. Theapertures may be circular apertures 612 of varying sizes. Additionallyor alternatively, the apertures may be irregular apertures 614. Thevarious circular apertures 612 and the irregular aperture 614 may beselectable. For example, the opaque material 610 may be on a mechanicalstage (e.g., a rotational stage or a translational stage) that can movewith respect to a lens (e.g., the lens 130 illustrated in FIG. 1A) andan array of light detectors (e.g., the array 110 of light detectors 112illustrated in FIG. 1A) so as to select one of the apertures.

The circular apertures 612 may vary in radius, thereby allowing varyingamounts of light to pass through the respective apertures. In someembodiments, the larger radius apertures may allow for increasedillumination of the array of light detectors, which may lead to anincreased sensitivity of a corresponding noised limiting system (e.g.,the noise limiting system 110 illustrated in FIG. 1A). However, whenmeasuring scenes having an increased amount of background light, thecircular apertures 612 having smaller radius may be used to block agreater proportion of the background light. Further, each of thecircular apertures 612 may have different associated optical filters(e.g., overlaying the respective aperture or embedded within therespective aperture). For example, one of the circular apertures 612 mayselectively transmit light within a visible wavelength range, andanother of the circular apertures 612 may selectively transmit lightwithin an infrared wavelength range. As such, a single opaque material610, having multiple circular apertures 612 defined therein, may becapable of selectively transmitting light emitted from various sources(e.g., various laser emitters 212, as illustrated in FIG. 2). Variouscircular apertures 612 having various associated optical filters mayhave similar or different radii.

Irregular apertures may be specifically designed to account for opticalaberrations within a system. For example, the keyhole shape of theirregular aperture 614 illustrated in FIG. 6A may assist in accountingfor parallax occurring between an emitter (e.g., the laser emitter 212illustrated in FIG. 2) and a receiver (e.g., the lens 130 and the array110 of light detectors illustrated in FIG. 2 with the opaque material610 located therebetween). The parallax may occur if the emitter and thereceiver are not located at the same position, for example. Otherirregular apertures are also possible, such as specifically shapedapertures that correspond with particular objects expected to be withina particular scene or irregular apertures that select for specificpolarizations of light (e.g., horizontal polarizations or verticalpolarizations).

FIG. 6B is an illustration of a portion of a noise limiting system thatincludes apertures, according to example embodiments. Similar to thenoise limiting system 100 of FIG. 1A, the noise limiting system mayinclude a lens 130. The noise limiting system may additionally includean opaque material 650 with apertures 652 defined therein, and anadjustable MEMS mirror 660. The system may measure light 102 scatteredby an object 140 within a scene.

The opaque material 650, similar to the opaque material 120 illustratedin FIG. 1A, may block the light 102 from the scene (e.g., backgroundlight) that is focused by the lens 130 from being transmitted to anarray (e.g., the array 110 illustrated in FIG. 1A). The opaque material650, and therefore the apertures 652 may be located with respect to theMEMS mirror 660 and the lens 130 such that the surface of the opaquematerial 650 is located at or near the focal plane of the lens 130.Similar to the embodiment of the opaque material 120 illustrated in FIG.1A, the opaque material 650 may include a metal layer, a polymersubstrate, a BoPET sheet, or a glass overlaid with an opaque mask.

The apertures 652, as illustrated, may be circular. In alternateembodiments, the apertures may be different shapes or sizes.Additionally or alternatively, in some embodiments there may be more orfewer apertures than illustrated in FIG. 6B. The apertures 652 may bealigned with respect to the MEMS mirror 660, such that a portion of thelight 102 reflected by the MEMS mirror 660 passes through one of theapertures 652 and then intercepts an array of light detectors (e.g., thearray 110 of light detectors 112 illustrated in FIG. 1A).

The MEMS mirror 660 may reflect the light 102 that is focused by thelens 130. The MEMS mirror 660 may rotate about multiple axes such thatthe reflected light 102 is directed toward a specific one, or multiple,of the apertures 652. In some embodiments, the rotation of the MEMSmirror 660 may be controlled by a computing device (e.g., amicrocontroller). Further, in alternate embodiments, there may be a setof MEMS mirrors that sequentially reflect the light to direct the lighttoward one, or multiple, of the apertures. Multiple MEMS mirrors couldbe located on a single MEMS microchip or across multiple MEMSmicrochips, for example.

In alternate embodiments, the MEMS mirror (or other type of mirror) mayreplace the opaque material with the multiple apertures. For example, areflective surface of the MEMS mirror (or MEMS mirror array) may besurrounded by an opaque material and the reflective surface may act todefine an aperture. As such, the MEMS mirror may select a portion of thelight, which is focused by the lens, to reflect toward the array. Theunselected portion of the light may be absorbed by the opaque material,for example. In such example embodiments, the lens and the array may bedisposed on the same side of the mirror. Further, in such embodimentswhere the mirror is a MEMS mirror array, the elements in the MEMS mirrorarray could be selectively switched to dynamically define a shape, aposition, or a size of the reflective surface that defines the aperture.

FIG. 7A is an illustration of an opaque material 710 with a resizableaperture, according to example embodiments. The opaque material 710 mayhave a slit 712 defined therein. Overlaying the opaque material 710there may be an opaque shutter 714. The aperture may be adjusted in sizeby moving the opaque shutter 714 relative to the opaque material 710,thereby varying the covered portion of the slit 712. In such a way, theaperture size could be adjusted without varying the direction ofprojection of light (e.g., as is done in the embodiment illustrated inFIG. 6B) within a noise limiting system 100.

The opaque material 710, similar to the opaque material 120 illustratedin FIG. 1A, may block light from the scene from being transmitted to anarray (e.g., the array 110 illustrated in FIG. 1A). The opaque material710 may be located at the focal plane of a lens, in some embodiments.

The slit 712, without the opaque shutter 714, is analogous to theaperture of other embodiments. For example, if the opaque material 710is a piece of glass overlaid by an opaque mask, the slit 712 is thenegative region of the mask (i.e., the region of the mask where theremask material has been removed, e.g., by photolithography). Further, thedimensions of the slit 712 define the largest aperture size for acorresponding noise limiting system. As such, the size of the slit 712is equivalent to the size of the aperture when the opaque shutter 714has been fully retracted from covering the slit 712. In alternateembodiments, the slit could have a different shape. For example, theslit may be shaped so that when the opaque shutter is translatedlinearly over the slit, the size of the slit increases or decreasesexponentially. Alternatively, the slit may be circularly shaped orirregularly shaped (e.g., keyhole shaped, such as the irregular aperture614 illustrated in FIG. 6A). In still other embodiments, there could bemultiple slits, which could be selected from and/or adjusted in sizebased on the location of the opaque shutter.

The opaque shutter 714 is a material that may be absorptive and/orreflective to a range of wavelengths of light. The range of wavelengthsmay include wavelengths of background light within a scene (e.g., if theopaque shutter 714 is a component of a noise limiting system within aLIDAR device). In some embodiments, the opaque shutter 714 could includea metal sheet, a BoPET sheet, or a polymer substrate. The opaque shutter714 may be configured to move with respect to the opaque material 710and the slit 712. For example, in some embodiments the opaque shutter714 may be attached to a mechanical stage that can move translationallywith respect to the opaque material 710 and the slit 712. Such movementmay be controlled by a computing device (e.g., a microcontroller). Inalternate embodiments, the opaque material and the slit may, instead,move with respect to the opaque shutter (e.g., the opaque material andthe slit are attached to a mechanical stage, rather than the opaqueshutter).

FIG. 7B is an illustration of an opaque material 760 with a resizableaperture, according to example embodiments. The opaque material 760 maybe embedded with an iris 762. The iris 762 and the opaque material 760may be fabricated out of the same or different materials. The aperturemay be an opening defined by the iris 762. Further, the iris 762 mayexpand or contract to adjust the size of the aperture. In such a way,the aperture size could be adjusted without varying the direction ofprojection of light (e.g., as is done in the embodiment illustrated inFIG. 6B) within a noise limiting system 100. In some embodiments, theiris may be a standalone free-space optical component, rather than beingembedded within an opaque material.

The iris 762 may be defined with multiple opaque fins (e.g., sixteenopaque fins as illustrated in FIG. 7B) that extend or retract to adjustthe size of the aperture defined by the iris 762. The iris 762 may be aMEMS iris, in some embodiments. The opaque fins may be metallic, forexample. Further, in some embodiments, the extension or retraction ofthe fins of the iris 762 may be controlled by a computing device (e.g.,a microcontroller). A maximum extension of the opaque fins may result inthe aperture having a minimum size. Conversely, a maximum retraction ofthe opaque fins may result in the aperture having a maximum size.

In alternate embodiments, the opaque material may include an active orpassive matrix of liquid crystal light modulators, rather than an iris.In some embodiments, the matrix may include a patterned conductiveelectrode array with two polarizers. Between the two polarizers may bealignment layers and a liquid crystal layer. Such an arrangement may besimilar to a liquid crystal display device. The matrix could define theaperture within the opaque material. For example, the matrix could bearbitrarily adjusted (e.g., by a computing device) to select a size, aposition, or a shape of the aperture. Additionally, in some embodiments,the optical filter may be integrated within the matrix (e.g., on top oron bottom of the matrix, or sandwiched between layers of the matrix).

FIG. 8 is an illustration of an opaque material 810 with an aperture 812having an adjustable location, according to example embodiments. Forexample, the opaque material 810 may translate in a two-dimensionalplane, relative to a lens and an array of light detectors (e.g., thelens 130 and the array 110 of light detectors 112 within the noiselimiting system 100 illustrated in FIG. 1A), to move the aperture 812.The opaque material 810 may be driven by a stage or an electric motor,in various embodiments. Further, such a stage or electric motor may becontrolled by a computing device (e.g., a microcontroller). Similar tothe opaque material 120 illustrated in FIG. 1A, the opaque material 810may be etched metal, a BoPET sheet, or a glass overlaid with an opaquemask. Other materials are also possible.

The aperture 812 may be a circular aperture, as illustrated in FIG. 8.Alternatively, the aperture may have another shape, such as an oval, arectangle, or an irregular shape (e.g., a keyhole shape similar to theshape of the irregular aperture 614 illustrated in FIG. 6A). Further, insome embodiments, the opaque material may have multiple aperturesdefined therein (e.g., similar to the opaque material 610 illustrated inFIG. 6A).

III. Example Processes

FIG. 9 is a flow chart illustration of a method 900, according toexample embodiments. The method 900 may be performed by the noiselimiting system 100 illustrated in FIG. 1A, for example.

At block 902, the method 900 includes focusing, by a lens (e.g., thelens 130 illustrated in FIG. 1A) disposed relative to a scene, lightfrom the scene onto a focal plane. The light from the scene may bescattered by an object (e.g., the object 140 illustrated in FIG. 1A)within the scene, in some embodiments.

At block 904, the method 900 includes transmitting, through an aperture(e.g., the aperture 122 illustrated in FIG. 1A) defined within an opaquematerial (e.g., the opaque material 120 illustrated in FIG. 1A) disposedat the focal plane of the lens, the light from the scene. The aperturehas a cross-sectional area.

At block 906, the method 900 includes diverging, by the light from thescene transmitted through the aperture.

At block 908, the method 900 includes intercepting, by an array of lightdetectors disposed on a side of the focal plane opposite the lens, thediverged light from the scene. A cross-sectional area of the array oflight detectors that intercept the diverged light from the scene isgreater than the cross-sectional area of the aperture.

At block 910, the method 900 includes detecting, by the array of lightdetectors, the intercepted light.

IV. Conclusion

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. While various aspects and embodiments have beendisclosed herein, other aspects and embodiments will be apparent. Thevarious aspects and embodiments disclosed herein are for purposes ofillustration only and are not intended to be limiting, with the truescope being indicated by the following claims.

What is claimed:
 1. A system, comprising: a lens disposed relative to ascene and configured to focus light from the scene onto a focal plane;an aperture defined within an opaque material disposed at the focalplane of the lens, wherein the aperture has a cross-sectional area; andan array of light detectors disposed on a side of the focal planeopposite the lens and configured to intercept and detect diverging lightfocused by the lens and transmitted through the aperture, wherein across-sectional area of the array of light detectors that intercepts thediverging light is greater than the cross-sectional area of theaperture.
 2. The system of claim 1, wherein the array of light detectorscomprises a plurality of single photon avalanche diodes (SPADs).
 3. Thesystem of claim 1, wherein the light detectors in the array areconnected in parallel with one another.
 4. The system of claim 1,wherein the cross-sectional area of the aperture is adjustable.
 5. Thesystem of claim 4, wherein the opaque material comprises an irisconfigured to define the cross-sectional area of the aperture.
 6. Thesystem of claim 4, wherein the opaque material comprises a patternedconductive electrode array having two polarizers; one or more alignmentlayers disposed between the two polarizers; and a liquid crystal layerdisposed between the two polarizers.
 7. The system of claim 1, whereinthe light from the scene is light scattered by one or more objects beingilluminated by a transmitter of a light detection and ranging (LIDAR)system.
 8. The system of claim 1, further comprising a mirror configuredto reflect the light from the scene transmitted through the aperturetoward the array of light detectors.
 9. The system of claim 1, whereinthe light detectors are sensitive to light within a range ofwavelengths.
 10. The system of claim 1, wherein the light detectors aresensitive to light having infrared wavelengths.
 11. The system of claim1, further comprising a filter configured to divert light from the scenewithin one or more wavelength ranges away from the aperture so the lightfrom the scene within the one or more wavelength ranges does not passthrough the aperture.
 12. The system of claim 1, wherein the opaquematerial comprises an opaque mask overlaying a glass substrate.
 13. Thesystem of claim 1, wherein the opaque material comprises a metal, andwherein the metal is etched to define the aperture.
 14. The system ofclaim 1, wherein each light detector occupies a cross-sectional area ofbetween 200 μm² and 600 μm².
 15. The system of claim 1, furthercomprising a diffuser disposed between the array of light detectors andthe aperture, wherein the diffuser is configured to diffuse the lightfrom the scene transmitted through the aperture evenly across the arrayof light detectors.
 16. The system of claim 1, wherein the aperture isselectable from a set of two or more apertures.
 17. The system of claim16, further comprising one or more microelectromechanical systems (MEMS)mirrors adjustable to direct the light from the scene toward theaperture to select from the set of two or more apertures.
 18. The systemof claim 1, wherein the aperture has a non-circular shape.
 19. Thesystem of claim 1, further comprising a structure, disposed in betweenthe aperture and the array of light detectors, which totally internallyreflects the diverging light transmitted through the aperture.
 20. Thesystem of claim 1, wherein a location of the aperture in the focal planeis adjustable.
 21. The system of claim 1, wherein the aperture comprisesan array of selectively switchable MEMS mirrors.
 22. A method,comprising: focusing, by a lens disposed relative to a scene, light fromthe scene onto a focal plane; transmitting, through an aperture definedwithin an opaque material disposed at the focal plane of the lens, thelight from the scene, wherein the aperture has a cross-sectional area;diverging, by the light from the scene transmitted through the aperture;intercepting, by an array of light detectors disposed on a side of thefocal plane opposite the lens, the diverged light from the scene,wherein a cross-sectional area of the array of light detectors thatintercept the diverged light from the scene is greater than thecross-sectional area of the aperture; and detecting, by the array oflight detectors, the intercepted light.
 23. A light detection andranging (LIDAR) device, comprising: a LIDAR transmitter configured toilluminate a scene with light; a LIDAR receiver configured to receivelight scattered by one or more objects within the scene to map thescene, wherein the LIDAR receiver comprises: a lens configured to focusthe light scattered by the one or more objects within the scene onto afocal plane; an aperture defined within an opaque material disposed atthe focal plane, wherein the aperture has a cross-sectional area; and anarray of light detectors disposed on a side of the focal plane oppositethe lens and configured to intercept and detect diverging light focusedby the lens and transmitted through the aperture, wherein across-sectional area of the array of light detectors that intercepts thediverging light is greater than the cross-sectional area of theaperture.